William Backhouse Astor, Jr. (July 12, 1829 – April 25, 1892) was a businessman, racehorse breeder/owner, and yachtsman. He was also a member of the prominent Astor family. While his elder brother financier/philanthropist John Jacob Astor III (1822–1890) was head of the English line of Astors, William Jr. was the patriarch of the male line of American Astors.